1. Field of the Invention
This invention relates to microstrip transmission lines and dielectric waveguides operating in the millimeter wave region of the frequency spectrum and more particularly to a transition for providing a low loss, broad band interconnection between such microstrip transmission lines and dielectric waveguides.
2. Description of the Prior Art
Planar type circuitry using microstrip is widely used in millimeter wave frequency applications because it permits the design of equipment having extremely small size and low weight which is desirable for many items of military and commercial equipment such as radar systems, for example. Unfortunately, planar type circuitry is inconvenient or not available with presently known technology for performing many functions such as the functions performed by phase shifters and antennas, for example. These functions are usually performed in millimeter wave frequency applications by equipment utilizing dielectric waveguide such as ferrite rod phase shifters and dielectric waveguide antennas, for example. In order to connect the microstrip transmission line of the planar circuitry to the solid dielectric waveguide for such applications, resort is usually had to a section of hollow, metallic waveguide. The end of the section of hollow, metallic waveguide which is to be coupled to the microstrip transmission line is usually provided with a metal ridge waveguide of the type described in an article entitled "Straightforward Approach Produces Broadband Transitions" by D. R. Singh and C. R. Seashore which appeared in the September, 1984 issue of the "Microwaves & RF Magazine". The other end of the section of hollow, metallic waveguide which is coupled to the dielectric waveguide is provided with impedance transformer means which matches the impedance of the metal waveguide to the impedance of the dielectric waveguide. As is well known in the art, the impedance transformer may comprise a section of the dielectric waveguide which projects a short distance into the hollow, metallic waveguide and which is tapered. It is apparent that this transition arrangement involves not only the microstrip to dielectric waveguide loss but also the microstrip to metallic waveguide guide transition loss, the metallic waveguide loss and the metallic waveguide to dielectric waveguide transition loss. Additionally, the transition equipment is relatively complex to fabricate and adds to the size and weight of the overall equipment.